1. Field of the Invention
The subject invention is related to a push button for an inductive value input keyboard, having a push-button socket, a push-button head guided in the push-button socket, a compression spring with stop means acting between the push-button socket and the push-button head, the stop means limiting the stroke of the push button in a non-actuated state, and a rod-shaped iron core fastened to the push-button head for acting with an induction coil formed by conductor paths upon a printed circuit board on which the push button is located.
2. Description of Related Art
In known push button designs, the push-button head consists of a cover cap and a support at which the guidance shaft of the push button is molded, and in which apertures are formed into which locks or detent hooks molded at the socket of the push button engage for the purpose of arresting the push-button head in the end position. An iron or ferrite pin of high permeability for signal generation is usually embedded in the support by injection molding.
The apertures and the locks, as well as the opposed submerged openings and sink marks, in the support can be faced or closed off towards the outside by means of the cover cap without any problems. During the embedding process of the ferrite pins there exists, additionally, the danger that, on the one hand, the receptacle for the ferrite pins in the injection mould wears out relatively rapidly because of the hardness of the ferrite pins and thus resulting in no acceptable positional tolerances, and, on the other hand, there is the danger that splinters, which chip off when handling the relatively brittle ferrite pins, can interfere with the positive locking.
If the push-button head is fabricated as one part, in order to achieve as shallow as possible a construction suitable for quantity production, an embedding of the ferrite pin is not possible because of the danger of sink marks. In this case, the ferrite pin must be pressed into a suitable mounting, which, in the case of a ferrite pin, is only possible with accuracy requiring a great effort, or it has to be bonded in, which, in quantity production, particularly if a mechanical installation of the push button is desired, results in an unsuitable fabrication process.